Dual-specificity phosphatase 29 is induced during neurogenic skeletal muscle atrophy and attenuates glucocorticoid receptor activity in muscle cell culture

Parental cardiorespiratory fitness influences early life energetics and metabolic health

High cardiorespiratory fitness (CRF) is associated with a reduced risk of metabolic disease and is linked to superior mitochondrial respiratory function. This study investigated how intrinsic CRF affects bioenergetics and metabolic health in adulthood and early life. Adult rats selectively bred for low and high running capacity [low capacity runners (LCR) and high capacity runners (HCR), respectively] underwent metabolic phenotyping before mating. Weanlings were evaluated at 4-6 wk of age, and whole body energetics and behavior were assessed using metabolic cages. Mitochondrial respiratory function was assessed in permeabilized tissues through high-resolution respirometry. Proteomic signatures of adult and weanling tissues were determined using mass spectrometry. The adult HCR group exhibited lower body mass, improved glucose tolerance, and greater physical activity compared with the LCR group. The adult HCR group demonstrated higher mitochondrial respiratory capacities in the soleus and heart compared with the adult LCR group, which coincided with a greater abundance of proteins involved in lipid catabolism. HCR and LCR weanlings had similar body mass, but HCR weanlings displayed reduced adiposity. In addition, HCR weanlings exhibited better glucose tolerance and higher physical activity levels than LCR weanlings. Higher respiratory capacities were observed in the soleus, heart, and liver tissues of HCR weanlings compared with LCR weanlings, which were not owed to greater mitochondrial content. Proteomic analyses indicated a greater potential for lipid oxidation in the contractile muscles of HCR weanlings. In conclusion, offspring born to parents with high CRF possess an enhanced capacity for lipid catabolism and oxidative phosphorylation, thereby influencing metabolic health. These findings highlight that intrinsic CRF shapes the bioenergetic phenotype with implications for metabolic resilience in early life.NEW & NOTEWORTHY Inherited cardiorespiratory fitness (CRF) influences early life bioenergetics and metabolic health. Higher intrinsic CRF was associated with reduced adiposity and improved glucose tolerance in early life. This metabolic phenotype was accompanied by greater mitochondrial respiratory capacity in skeletal muscle, heart, and liver tissue. Proteomic profiling of these three tissues further revealed potential mechanisms linking inherited CRF to early life metabolism.

Multi-omic identification of key transcriptional regulatory programs during endurance exercise training

Transcription factors (TFs) play a key role in regulating gene expression and responses to stimuli. We conducted an integrated analysis of chromatin accessibility, DNA methylation, and RNA expression across eight rat tissues following endurance exercise training (EET) to map epigenomic changes to transcriptional changes and determine key TFs involved. We uncovered tissue-specific changes and TF motif enrichment across all omic layers, differentially accessible regions (DARs), differentially methylated regions (DMRs), and differentially expressed genes (DEGs). We discovered distinct routes of EET-induced regulation through either epigenomic alterations providing better access for TFs to affect target genes, or via changes in TF expression or activity enabling target gene response. We identified TF motifs enriched among correlated epigenomic and transcriptomic alterations, DEGs correlated with exercise-related phenotypic changes, and EET-induced activity changes of TFs enriched for DEGs among their gene targets. This analysis elucidates the unique transcriptional regulatory mechanisms mediating diverse organ effects of EET.

Zebrafish Model for Studying Dexamethasone-Induced Muscle Atrophy and Preventive Effect of Maca (Lepidium meyenii)

Loss of myofibers during muscle atrophy affects functional capacity and quality of life. Dexamethasone, an inducer of rapid atrophy of skeletal myofibers, has been studied as a glucocorticoid receptor in muscle atrophy or motor neurodegeneration. In this study, we examined dexamethasone-induced muscle atrophy using zebrafish (Danio rerio), a vertebrate model, and assessed whether administration of Lepidium meyenii (maca) as a dietary supplement can prevent muscle atrophy. Changes in skeletal myofibers in zebrafish were evaluated after exposure to dexamethasone for different periods and at different concentrations. Under optimized conditions, zebrafish pre-fed with maca for 3 days were exposed to 0.01% dexamethasone for 1 h/day for 7 days. Thereafter, myofiber loss, damaged muscle contractile proteins, and abnormal exploratory behavior due to the structural and functional impairment of skeletal muscle associated with muscle atrophy were investigated using hematoxylin-eosin, immunofluorescence staining, and behavioral analyses. Our findings suggest that dexamethasone induces muscle atrophy in zebrafish, inhibiting exploratory behavior by inducing myofiber loss, inhibiting muscle contraction, and causing changes in endurance and velocity. Thus, the zebrafish model can be used to screen pharmaceutical agents and to study muscle atrophy. Furthermore, maca is a potential dietary supplement to prevent muscle atrophy, as it protects muscle fibers.

FGGY carbohydrate kinase domain containing is expressed and alternatively spliced in skeletal muscle and attenuates MAP kinase and Akt signaling

Skeletal muscle atrophy can result from a range of physiological conditions, including denervation, immobilization, hindlimb unweighting, and aging. To better characterize the molecular genetic events of atrophy, a microarray analysis revealed that FGGY carbohydrate kinase domain containing (Fggy) is expressed in skeletal muscle and is induced in response to denervation. Bioinformatic analysis of the Fggy gene locus revealed two validated isoforms with alternative transcription initiation sites that we have designated Fggy-L-552 and Fggy-S-387. Additionally, we cloned two novel alternative splice variants, designated Fggy-L-482 and Fggy-S-344, from cultured muscle cells suggesting that at least four Fggy splice variants are expressed in skeletal muscle. Quantitative RT-PCR was performed using RNA isolated from muscle cells and primers designed to distinguish the four alternative Fggy transcripts and found that the Fggy-L transcripts are more highly expressed during myoblast differentiation, while the Fggy-S transcripts show relatively stable expression in proliferating myoblasts and differentiated myotubes. Confocal fluorescent microscopy revealed that the Fggy-L variants appear to localize evenly throughout the cytoplasm, while the Fggy-S variants produce a more punctuate cytoplasmic localization pattern in proliferating muscle cells. Finally, ectopic expression of Fggy-L-552 and Fggy-S-387 resulted in inhibition of muscle cell differentiation and attenuation of the MAP kinase and Akt signaling pathways. The identification and characterization of novel genes such as Fggy helps to improve our understanding of the molecular and cellular events that lead to atrophy and may eventually result in the identification of new therapeutic targets for the treatment of muscle wasting.